Centrifugal fans



Oct. 18, 1960 MAYER JR" ETAL 2,956,736

CENTRIFUGAL FANS Filed May 14, 1959 INVENTORS MAYER MAYER, Jr. JAMES l.KOTTER ATTORNEYS United States Patent CENTRIFUGAL FANS Mayer Mayer, Jr.,New Orleans, and James I. Kotter, Metairie, La., assignors to the UnitedStates of America as represented by the Secretary of Agriculture FiledMay 14, 1959, Ser. No. 813,317

1 Claim. (Cl. 230-127) (Granted under Title 35, US. Code (1952), sec.266) A non-exclusive, irrevocable, royalty-free license in the inventionherein described, throughout the world for all purposes of the UnitedStates Government, with the power to grant sub-licenses for suchpurposes, is hereby granted to the Government of the United States ofAmerica.

This invention relates to centrifugal fans.

A centrifugal fan comprises a spiral fan housing provided with an outletport, a fan wheel rotatably mounted in said housing and provided withfan blades, and a point of cutoff where the flow of air is dischargedthrough said outlet port. In the operation of such a fan, air enters thefan housing through an air inlet opening and is thrust between the fanblades. As the fan wheel rotates, the blades propel the air through thehousing past the point of cutoff where the air is discharged through theoutlet port.

Objectionable noise is created at the point of cutoff and, in order tominimize this noise, it is standard practice to utilize a fan wheel ofsuch diameter that the free ends of each of the fan blades clears thepoint of cutoff by an appreciable distance.

However, while such positioning of the blades tends to reduce noise italso detrimentally influences fan efficiency and makes it necessary toutilize a fan of greater size than would be required if the free ends ofthe blades ran close to the point of cutoff.

The instant invention has as its object the provision of a centrifugalfan having greatly decreased noise at the point of cutoff, as well ashigh fan efiiciency.

These objects are accomplished by providing a centrifugal fan in which aspecially shaped end portion of the housing wall having a camberedsurface of particularly critical dimensions, as will be describedhereinafter, and having a rounded leading edge which serves as a pointof cutoff, permits spacing of the free outer ends of the fan blades ofthe fan wheel so that they run close to said leading edge.

In the accompanying drawing,

Fig. 1 is a cross-section of a centrifugal fan illustrating theinvention; and

Fig. 2 is an enlarged view of the specially shaped end portion of thehousing wall.

Referring to the drawing,

Fig. 1 illustrates a centrifugal fan having a fan housing comprising aperipheral wall 11. A fan wheel 12, having radial blades 13 with freeouter ends, is rotatably mounted in the housing on a shaft 14 driven bya power source not shown.

The housing wall 11 has an airfoil-shaped end portion 20 extending in anupstream direction, that is, in a direction opposed to the direction ofrotation of blades 13. This airfoil-shaped end portion is provided witha rounded leading free edge 21 having close running Patented Oct. 18,1960 clearance with the free outer ends of the blades 13 to give highfan efliciency. The airfoil-shaped end portion is joined at its otheredge to the remainder 22 of housing wall 11 to form a line of jointureat 23, the said remainder wall portion 22 being spaced radiallyoutwardly from the free outer ends of the blades 13 and encircling thefan wheel in a spiral formation.

As a result of this structure, the housing is provided with an outletport for the egress of air, this outlet port being defined as theopening included between the leading edge 21 of the airfoil-shaped endportion 20 and the spiral wall of the housing opposite thereto. Theoutlet port communicates with a duct 25 to carry away the dischargedair.

The airfoil-shaped end portion 20 also has a cambered surface on itsside 30 remote from the fan wheel, as shown in Fig. 1, while its otherside 31 may have a surface of any shape. As illustrated in Fig. 1, side31 has a surface contoured to the shape of the spiral housing.

The dimensions of the cambered surface of side 30 are such that A rangesfrom .10 to .20 of C and X ranges from .20 to .45 of C, wherein C is thedistance from leading edge 21 to the line of jointure at 23 of theairfoilshaped end portion 20 to the remainder 22 of the spiral wall ofthe housing, A is the perpendicular distance from the highest point 35of said cambered surface of side 30 to a base line 36 drawn from saidleading edge to said line of jointure at 23, and X is the distance fromsaid highest point 35 of said cambered surface to a line 37 drawnperpendicular through said leading edge to said base line 36.

As a specific example of a highly satisfactory fan, the dimensions ofthe cambered surface of side 30 are such that A is inch, X is inch, C is2% inches, and the overall diameter of the fan wheel is 10 inches. Inthis example, C may range from 1 /8 inches to 3% inches for a fan havingan overall diameter of 10 inches.

In operation, air enters the housing through air inlet opening 40. Asthe fan wheel rotates, the fan blades 13 propel the air through thehousing past the leading edge 21 of the airfoil-shaped end portion 20.The latter, by virtue of its critical shape, functions to decrease thenoise of the moving air as it is discharged through the outlet port,with the fan operating at high efficiency. Thus, in effect, the leadingedge serves as the point of cutoff in the housing.

Having thus described the invention, what is claimed A centrifugal fancomprising a housing, a fan wheel rotatably mounted in the housing andhaving radial blades with free outer ends, said housing comprising aperipheral wall having an airfoil-shaped end portion extending in anupstream direction and being provided with a rounded leading free edgehaving a close running clearance with the free outer ends of said bladesto give high fan efficiency, said airfoil-shaped end portion beingjoined at its other edge to the remainder of said wall, said remainderwall portion being spaced radially outwardly from said free outer endsof the blades and encircling the fan wheel in a spiral formation, anoutlet port for the housing, said outlet port being defined as theopening included between said leading free edge of the airfoil-shapedend portion and the spiral wall of the housing opposite thereto, saidairfoil-shaped end portion having, in addition to its rounded leadingedge, a cambered surface on its side remote from the fan wheel in whichA ranges from .10 to .20 of C and X ranges from .20 to .45 of C, whereinC is the distance from said lead- 3 4 ing edge to the line of jointureof the airfoil-shaped and References Cited in the file of this patentportion to the remainder of the spiral wall of the housing, UNITEDSTATES PATENTS A is the perpendicular distance from the highest point 2596 646 Buchi May 13 1952 of said cambered surface to a base line drawnfrom said 5 2:596:647 Buchi May 1952 leading edge to said line ofjointure, and X is the distance from said highest point of said camberedsurface to a FOREIGN PATENTS line drawn perpendicular through saidleading edge to 278,711 Switzerland Feb. 1, 1952 said base line.1,038,819 France May 13, 1953

